THE CLUSTER LENSING AND SUPERNOVA SURVEY WITH HUBBLE: AN OVERVIEW

Abstract

The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit\nmulti-cycle treasury program to use the gravitational lensing properties of 25\ngalaxy clusters to accurately constrain their mass distributions. The survey,\ndescribed in detail in this paper, will definitively establish the degree of\nconcentration of dark matter in the cluster cores, a key prediction of CDM. The\nCLASH cluster sample is larger and less biased than current samples of\nspace-based imaging studies of clusters to similar depth, as we have minimized\nlensing-based selection that favors systems with overly dense cores.\nSpecifically, twenty CLASH clusters are solely X-ray selected. The X-ray\nselected clusters are massive (kT > 5 keV; 5 - 30 x 10^14 M_solar) and, in most\ncases, dynamically relaxed. Five additional clusters are included for their\nlensing strength (Einstein radii > 35 arcsec at z_source = 2) to further\nquantify the lensing bias on concentration, to yield high resolution dark\nmatter maps, and to optimize the likelihood of finding highly magnified\nhigh-redshift (z > 7) galaxies. The high magnification, in some cases, provides\nangular resolutions unobtainable with any current UVOIR facility and can yield\nz > 7 candidates bright enough for spectroscopic follow-up. A total of 16\nbroadband filters, spanning the near-UV to near-IR, are employed for each\n20-orbit campaign on each cluster. These data are used to measure precise\n(sigma_phz < 0.02(1+z)) photometric redshifts for dozens of newly discovered\nmultiply-lensed images per cluster. Observations of each cluster are spread\nover 8 epochs to enable a search, primarily in the parallel fields, for Type Ia\nsupernovae at z > 1 to improve constraints on the time dependence of the dark\nenergy equation of state and the evolution of such supernovae in an epoch when\nthe universe is matter dominated.\n